Jostling for position: Competition at the root of diversity in rainforests

Date:

January 26, 2012

Source:

Ludwig-Maximilians-Universitaet Muenchen (LMU)

Summary:

Another attractive theory falls foul of the facts. A census of trees in rainforests on three continents has confirmed that competition plays a central role in structuring communities. This contradicts the so-called neutral theory in ecology, which views random fluctuations as the decisive factor.

Share:

Total shares:

FULL STORY

A census of trees in rainforests on three continents has confirmed that competition plays a central role in structuring communities. This contradicts the so-called neutral theory in ecology, which views random fluctuations as the decisive factor.

A census of trees in rainforests on three continents has confirmed that competition plays a central role in structuring communities. This contradicts the so-called neutral theory in ecology, which views random fluctuations as the decisive factor.

Another attractive theory falls foul of the facts. A census of trees in rainforests on three continents has confirmed that competition plays a central role in structuring communities. This contradicts the so-called neutral theory in ecology, which views random fluctuations as the decisive factor.

Ecologists are still arguing about the nature of the factors that determine the species composition of ecological communities. On the one hand, there are those who view interspecies competition as the key element. A second group of influential ecologists postulates that random fluctuations in population structure and rates of species dispersal play the dominant role, particularly in the biological communities found in species-rich tropical rainforests. LMU biologist Professor Susanne Renner, who is Director of the Botanic Garden and herbaria in Munich, and Professor Robert E. Ricklefs of the University of Missouri in St. Louis have now analyzed data from censuses of tree species in rainforests around the globe and also taken advantage of fossil evidence, allowing them to chart diversity in both space and time. Their findings show that variation in species richness among families is very similar in all tropical forests in spite of millions of years of independent evolution and diversification. This correspondence strongly suggests that community structure in rainforests cannot be attributed to the action of stochastic factors. "The high degree of similarity was a surprise even to us," says Renner. "The results can be regarded as a nail in the coffin of the neutral theory."

In even the best habitats, resources are inevitably limited. This means that species must compete with each other for access to them. And for many ecologists, interspecies competition for resources is the critical factor that determines the composition of the community found in a given environment. According to the principle of competitive exclusion, two species that depend on the same vital resource or ecological niche for their survival cannot stably coexist. The better adapted species will ultimately displace its competitor.

In contrast, what is known as "neutral" theory postulates that stochastic variations in factors such as the rate of dispersal and extinction of species determine the patterns of species abundance in different communities. The American ecologist Stephen Hubbell is the leading proponent of neutral theory, which he developed to explain species-rich communities, such as tropical rainforests.

In these environments it is not uncommon to find hundreds of tree species growing close together. Hubbell contends that this makes it very unlikely that segregation of ecological niches and the principle of competitive exclusion are the overriding forces that determine community structure. His neutral theory has received a great deal of attention in recent years.

LMU biologist Professor Susanne Renner and her American colleague Professor Robert Ricklefs have now challenged the theory with the help of quantitative data. In Central and South American, African and Asian rainforests, the two researchers compared the abundance patterns of different tree species growing in plots of between 25 and 55 hectares. In addition, they compared the relative abundance of different families of trees in a 55- to 65-year-old fossil flora from tropical Colombia with their representation there today.

On the basis of the neutral theory, which assigns a leading role to stochasticity, one would not expect to find much similarity in community structure over such a wide area and such a long span of time. However, the results of the new study show that when families are arranged in order of species richness, the rankings that emerge are very similar on all three continents.

"The correlation is statistically highly significant," says Renner. "So we have uncovered a very substantial degree of agreement between the seven forest plots; even the numbers of trees per unit area that belong to a given taxonomic family are similar in all three regions. Moreover, the families with the highest species diversity in the Colombian rainforests today were already dominant 50 million years ago. The findings are astonishingly clear-cut, and should suffice to rule out the neutral theory."

Ludwig-Maximilians-Universitaet Muenchen (LMU). "Jostling for position: Competition at the root of diversity in rainforests." ScienceDaily. ScienceDaily, 26 January 2012. <www.sciencedaily.com/releases/2012/01/120126142939.htm>.

Ludwig-Maximilians-Universitaet Muenchen (LMU). (2012, January 26). Jostling for position: Competition at the root of diversity in rainforests. ScienceDaily. Retrieved August 2, 2015 from www.sciencedaily.com/releases/2012/01/120126142939.htm

Ludwig-Maximilians-Universitaet Muenchen (LMU). "Jostling for position: Competition at the root of diversity in rainforests." ScienceDaily. www.sciencedaily.com/releases/2012/01/120126142939.htm (accessed August 2, 2015).

July 31, 2015  Resettlement projects in the Amazon are driving severe tropical deforestation, according to new research. Widely hailed as a socially responsible and 'innocuous' strategy of land redistribution, ... read more

July 29, 2015  Viewing aquarium displays led to noticeable reductions in blood pressure and heart rate, a research team found in the first study of its kind. They also noted that higher numbers of fish helped to ... read more

July 31, 2015  A new study examines how consuming the concentrated extract of thylakoids found in spinach can reduce hunger and cravings. Thylakoids encourage the release of satiety hormones, which is very ... read more

July 30, 2015  The behavior of fruit flies, which are commonly used in laboratory experiments, is altered by electric fields, new research shows. The research indicates that the wings of the insects are disturbed ... read more

July 31, 2015  Starvation early in life can alter an organism for generations to come, according to a new study in nematodes. The epigenetic effects are a 'bet-hedging strategy.' Famine survivors are smaller and ... read more

July 31, 2015  The humble butterfly could hold the key to unlocking new techniques to make solar energy cheaper and more efficient, pioneering new research has shown. By mimicking the v-shaped posture adopted by ... read more

Sep. 9, 2014  In tropical rainforests, most young trees grow spatially independent from their parent trees. This means that it is not possible to predict where seedlings will take root, and less specialized ... read more

July 30, 2014  Inspired by the Red Queen in Lewis Carroll's Through the Looking Glass, researchers have improved a 35-year-old ecology model to better understand how species evolve over decades to millions of ... read more

July 18, 2012  The word rainforest usually conjures up visions of brightly coloured birds and hyperactive monkeys swooping through a thick green canopy of leaves, vines and flowers. But rainforests are also found ... read more

May 5, 2011  For more than two hundred years, the question of why there are more species in the tropics has been a biological enigma. A particularly perplexing aspect is why so many species live together in a ... read more